Monolith-type membrane structures using a porous support having an array of parallel channels, typically in a cylindrical form, and a gas selective membrane coated on the inner surface of channel walls, offer a higher surface area packing density than a single-channel tube of the same diameter, leading to higher permeation flux. This results in a dramatic reduction of both the membrane cost per surface area and the engineering costs to assemble large surface areas of membrane modules. The structures can be used to solve significant energy and environmental problems; for example, H2 recovery from waste gas streams, H2 purification from a production gas mixture for fuel cells application, CO2 capture from flue gas streams for sequestration, and other separations. These separation applications often require high temperature for better separation performance.
When a mixture gas stream to be separated is supplied into the channels of a monolith ceramic membrane product, it is separated through the membranes coated on the channel walls, and thereafter passes through pores of the membranes and pores of the support to flow out to an external space. The surface area of two ends of the support exposed to the stream, which includes the end flat surface, and the exterior curved surface of the support, have no membrane coating and therefore need to be sealed with a sealing material in order to prevent the gas stream being treated from passing through the exposed surface area and then pores of the substrate and flowing out of the membrane rod. Separation function could not be achieved without seal coating on the end portion. For separation to occur it is necessary for the gas stream to enter the channels and flow through the channel walls and the outer porous wall of the substrate.
When low-temperature sealant materials such as epoxy or silicone are used, the two ends of the membrane rod must be extended to a low temperature region in order to avoid degradation of the sealant material. This means that some part of membrane is exposed to low temperature, leading to reduction of overall separation performance. US 2005/0173332 disclosed a porous honeycomb filter structure sealed at an end portion for solid/liquid separations, wherein a glass-based sealing material is applied only to the end flat surface by a stamping mechanism with use of a sponge.
Another approach is to use high-temperature sealing material to seal the support onto stainless steel tube or dense alumina tube, so the whole membrane can be exposed at high temperature. H. Lu et al., Materials Science and Engineering B, 141 (2007) pp. 55-60, describe the use of special sealants as high temperature binding agents to seal the perovskite membrane disc onto the stainless steel tube. Y. Gu et al., J. Membr. Sci., 306 (2007) 216-227, describe sealing two ends of the tubular membrane with two dense alumina tubes by a ceramic connection, while C. Zhang et al., J. Membr. Sci., 299 (2007) 261-267, used a silver sealing material. Y. Teraoka et al., Solid State Ionics, 177 (2006) 2245-2248, describes the use of a glass ring; a method that is difficult to apply to monolith membrane rods, especially with small size channels. This approach lacks flexibility as result of permanent connection between support and stainless steel or dense ceramic tubes.
Embodiments of the present invention provide techniques for addressing one or more of the packaging seal concerns mentioned above.